The present invention relates to a system for controlling the position of marine propulsion devices, and more particularly to a position control system for a transom extension mounting assembly for an outboard motor.
Marine propulsion devices, such as outboard motors and stern drives, are supported from a boat transom by a drive mounting assembly. Various types of drive mounting assemblies are known, as for example a transom bracket for mounting an outboard motor directly on a boat transom or a gimbal ring assembly for likewise mounting a stern drive unit directly to the transom. While the drive unit may be trimmed when mounted directly on a transom, the motor's vertical height cannot be changed beyond the somewhat limited amount resulting from trimming operation. Therefore, the drive unit is typically mounted in a compromise position at a fixed height which will provide the best possible performance. Another type of drive mounting assembly relates to one which is capable of selectively supporting an outboard motor in either raised or lowered positions wholly aft of the boat transom. Many of these latter transom extension types of mounting assemblies are of the general type which include a parallelogram linkage.
Recently, transom extension mounting assemblies have become increasingly popular on high performance outboard motor powered boats, including bass boats where a lower position of the motor improves initial boat acceleration, and a higher position enhances top speed by reducing gear case drag. Additionally, a higher motor position reduces draft, thereby enhancing shallow water operation. It is further known that relocating the motor aft of the transom improves the handling characteristics of most boats at high speeds. These devices also allow the boat to have a higher transom for improved safety in following-wave conditions and they allow boat builders to manufacture a common hull/transom design for both outboard and stern drive applications.
Examples of outboard motor mounting assemblies which support the outboard motor wholly aft of the boat transom are disclosed in the following United States patents:
______________________________________ U.S.Pat. No. Inventor Issue Date ______________________________________ 2,737,920 Heath 1956 2,782,744 Staley 1957 3,990,660 Pipoz 1976 4,013,249 Meyer et al 1977 4,168,818 Ellis 1979 4,306,703 Finze 1981 4,354,848 Hall et al 1982 4,363,629 Hall et al 1982 4,367,860 Strang 1983 4,384,856 Hall et al 1983 4,406,632 Blanchard 1983 4,406,634 Blanchard 1983 4,482,332 Emmons 1984 4,504,237 Blanchard 1985 ______________________________________
U.S. patent application Ser. No. 092,168, filed Sept. 2, 1987, Ser. No. 100,216, filed Sept. 23, 1987, and Ser. No. 103,508, filed Oct. 1, 1987, all of which are assigned to the assignee of this application, disclose outboard motor transom extension mounting assemblies utilizing a quadrilateral linkage arrangement to raise and lower the motor with respect to the transom. In particular, pending application Ser. No. 092,168 discloses the use of sensing means operatively connected to the fluid power assembly utilized to raise and lower the motor, which sensing means generates a signal representative of an undesirable water level to cause the motor to be raised to a higher position. The undesirable water level may result, for example, in boat launching or in following wave conditions caused by rapid deceleration.
U.S. Pat. No. 4,318,699 discloses a system for automatically trimming a marine drive unit in response to a sensed operating condition, such as engine speed. A trimming operation involves tilting the drive unit about a horizontal axis to optimally position the drive in on-plane and off-plane operation of the boat.
Another problem which has become more apparent with the increased use of transom extension mounting assemblies for outboard motors is engine damage which may occur due to a loss of cooling water pressure. The shallow draft at which the motor may be operated when lifted vertically to enhance performance, may inhibit the intake and circulation of engine cooling water. The loss of cooling water pressure may lead to engine overheating and, ultimately, to damage to the engine. However, at low engine speeds, marine propulsion devices typically operate at low cooling water pressure with no danger of detrimental overheating or engine loss.
Many marine propulsion devices, including some outboard motors, utilize an engine block temperature sensor to provide an engine temperature measurement to the boat operator. Some systems also utilize a temperature sensor signal representative of a dangerous overheat condition to sound an audible alarm.
However, it would be desirable to have a position control system for a marine propulsion device which would automatically lower a motor operating in a raised position in the event an undesirable operating condition occurs in the engine. In particular, a system automatically responsive to the overheating potential of high performance engines operating in a high lift/shallow draft mode would be most desirable.